Circuitry to prevent lithium plating within a lithium ion battery

ABSTRACT

A method of upgrading a work machine having a lead-acid battery coupled to a drive circuit and at least one motor is disclosed. In the method, a lead-acid battery is removed from the work machine. Then, a lithium-ion battery pack having a lithium ion battery and an environmental management circuit is connected to the work machine in circuit with the drive circuit and the at least one motor.

INCORPORATION BY REFERENCE

The present patent application is a divisional patent application ofU.S. Ser. No. 16/390,834, filed on Apr. 22, 2019, which claims priorityto and incorporates by reference the patent application identified byU.S. Ser. No. 62/661,370, filed on Apr. 23, 2018, and titled “CircuitryTo Prevent Lithium Plating Within a Lithium Ion Battery”, the entirecontent of both applications is hereby incorporated herein by reference.

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT

Not Applicable.

THE NAMES OF THE PARTIES TO A JOINT RESEARCH AGREEMENT

Not Applicable.

BACKGROUND OF THE INVENTION

A rechargeable battery, storage battery, secondary cell, or accumulatoris a type of electrical battery which can be charged, discharged into aload, and recharged many times, while a non-rechargeable or primarybattery is supplied fully charged, and discarded once discharged.Rechargeable batteries are composed of one or more electrochemicalcells. The term “accumulator” is used as it accumulates and storesenergy through a reversible electrochemical reaction. Rechargeablebatteries are produced in many different shapes and sizes, ranging frombutton cells to megawatt systems connected to stabilize an electricaldistribution network. Several different combinations of electrodematerials and electrolytes are used, including lead-acid, nickel cadmium(NiCd), nickel metal hydride (NiMH), lithium ion (Li-ion), and lithiumion polymer (Li-ion polymer).

Rechargeable batteries are used for many applications including poweringautomobiles, portable consumer devices, light vehicles (such asmotorized wheelchairs, golf carts, electric bicycles, and electricforklifts), tools, and uninterruptible power supplies. Emergingapplications in hybrid internal combustion-battery and electric vehiclesare driving the technology to reduce cost, weight, size, and increaselifetime. Grid energy storage applications use rechargeable batteriesfor load-leveling, storing electric energy at times of low demand foruse during peak periods, and for renewable energy uses, such as storingpower generated from photovoltaic arrays during the day to be used atnight. Load-leveling reduces the maximum power which a plant must beable to generate, reducing capital cost and the need for peaking powerplants.

Rechargeable batteries include a positive active material, a negativeactive material and in some cases an electrolyte. The positive activematerial and the negative active material are disposed in theelectrolyte. During charging, the positive active material is oxidized,producing electrons, and the negative material is reduced, consumingelectrons. These electrons constitute a current flow in a circuitexternal to the rechargeable battery. The electrolyte may serve as abuffer for internal ion flow between the electrodes, as in lithium-ionand nickel-cadmium cells, or the electrolyte may be an activeparticipant in the electrochemical reaction, as in lead-acid cells.

The energy used to charge rechargeable batteries usually comes from abattery charger using AC mains electricity, or an alternator driven by aseparate motive source such as an engine. Regardless of the source ofenergy, to store energy in a rechargeable battery, the rechargeablebattery has to be connected to a DC voltage source. This is accomplishedby connecting a negative terminal of the rechargeable battery to anegative terminal of a power source and a positive terminal of the powersource to a positive terminal of the rechargeable battery. Further, avoltage output of the power source must be higher than that of therechargeable battery, but not much higher: the greater the differencebetween the voltage of the power source and the battery's voltagecapacity, the faster the charging process, but also the greater the riskof overcharging and damaging the rechargeable battery.

Battery charging and discharging rates are often discussed byreferencing a “C” rate of current. The C rate is that which wouldtheoretically fully charge or discharge the battery in one hour. Forexample, trickle charging might be performed at C/20 (or a “20 hour”rate), while typical charging and discharging may occur at C/2 (twohours for full capacity).

In some cases, rechargeable battery packs are formed of multipleelectrochemical cells (hereinafter “cells”) that are connected togetherin a series or parallel configuration. The capacity within cells of thevarious rechargeable battery packs vary depending on the discharge rate.Some energy is lost in the internal resistance of cell components(plates, electrolyte, interconnections), and the rate of discharge islimited by the speed at which chemicals in the cell can move about. Forlead-acid cells, the relationship between time and discharge rate isdescribed by Peukert's law; a lead-acid cell that can no longer sustaina usable terminal voltage at a high current may still have usablecapacity, if discharged at a much lower rate. Data sheets forrechargeable cells often list the discharge capacity on 8-hour or20-hour or other stated time; cells for uninterruptible power supplysystems may be rated at 15 minute discharge.

Battery manufacturers' technical notes often refer to voltage per cell(VPC) for the individual cells that make up the battery. For example, tocharge a 12 V lead-acid battery (containing 6 cells of 2 V each) at 2.3VPC requires a voltage of 13.8 V across the battery's terminals.

Lithium plating is the formation of metallic lithium around the anode oflithium-ion batteries during charging. Plating, also called deposition,can cause lithium ion batteries to malfunction over time. One cause oflithium plating is charging a lithium ion battery in temperatures below15 degrees C.

Lead acid batteries are tolerant of charging below 15 degrees C. Leadacid batteries have been used to power forklifts. When the fork is beingraised, power is supplied to electric motors by a lead acid battery packmounted within the forklift. When the fork is being lowered, analternator generates electrical power, that is then directed to the leadacid battery pack to charge the battery pack. Recharging the batterypack upon lowering of the fork, extends the time between recharging thebattery pack.

It would be advantageous to be able to power a work machine havingbattery charging circuitry designed for use with a lead acid batterypack with a replacement battery pack constructed of lithium ionbatteries. Due to the characteristics of the lithium ion batteries, thiswould greatly extend the time between charging the battery pack. It isto such an improved work machine that the present disclosure isdirected.

BRIEF DESCRIPTION OF THE DRAWINGS

To assist those of ordinary skill in the relevant art in making andusing the subject matter hereof, reference is made to the appendeddrawings, which are not intended to be drawn to scale, and in which likereference numerals are intended to refer to similar elements forconsistency. For purposes of clarity, not every component may be labeledin every drawing.

FIG. 1 is a block diagram of an exemplary hardware configuration of partof a work machine in accordance with an embodiment of the presentdisclosure.

FIG. 2 is a block diagram of the electronics of a conventional lead-acidbattery powered work machine.

FIG. 3 is a block diagram of an exemplary battery pack, constructed inaccordance with the present disclosure, and configured to replace theconventional lead-acid battery in the work machine depicted in FIGS. 1and 2.

FIG. 4 is another block diagram of circuitry within the battery pack ofFIG. 3, and configured to detect at least one environmental parameterand control regenerative braking power based upon a level of the atleast one environmental parameter in accordance with the presentdisclosure.

DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS

Before explaining at least one embodiment of the inventive conceptsdisclosed herein in detail, it is to be understood that the inventiveconcepts are not limited in their application to the details ofconstruction and the arrangement of the components or steps ormethodologies set forth in the following description or illustrated inthe drawings. The inventive concepts disclosed herein are capable ofother embodiments, or of being practiced or carried out in various ways.Also, it is to be understood that the phraseology and terminologyemployed herein is for the purpose of description and should not beregarded as limiting the inventive concepts disclosed and claimed hereinin any way.

In the following detailed description of embodiments of the inventiveconcepts, numerous specific details are set forth in order to provide amore thorough understanding of the inventive concepts. However, it willbe apparent to one of ordinary skill in the art that the inventiveconcepts within the instant disclosure may be practiced without thesespecific details. In other instances, well-known features have not beendescribed in detail to avoid unnecessarily complicating the instantdisclosure.

As used herein, the terms “comprises,” “comprising,” “includes,”“including,” “has,” “having,” and any variations thereof, are intendedto cover a non-exclusive inclusion. For example, a process, method,article, or apparatus that comprises a list of elements is notnecessarily limited to only those elements, and may include otherelements not expressly listed or inherently present therein.

Unless expressly stated to the contrary, “or” refers to an inclusive orand not to an exclusive or. For example, a condition A or B is satisfiedby anyone of the following: A is true (or present) and B is false (ornot present), A is false (or not present) and B is true (or present),and both A and B is true (or present).

In addition, use of the “a” or “an” are employed to describe elementsand components of the embodiments disclosed herein. This is done merelyfor convenience and to give a general sense of the inventive concepts.This description should be read to include one or at least one and thesingular also includes the plural unless it is obvious that it is meantotherwise.

As used herein, qualifiers like “substantially,” “about,”“approximately,” and combinations and variations thereof, are intendedto include not only the exact amount or value that they qualify, butalso some slight deviations therefrom, which may be due to manufacturingtolerances, measurement error, wear and tear, stresses exerted onvarious parts, and combinations thereof, for example.

The term “battery unit” as used herein means an individual battery cell,or multiple battery cells permanently connected together to form amodule.

Finally, as used herein any reference to “one embodiment” or “anembodiment” means that a particular element, feature, structure, orcharacteristic described in connection with the embodiment is includedin at least one embodiment. The appearances of the phrase “in oneembodiment” in various places in the specification are not necessarilyall referring to the same embodiment.

Embodiments of the present invention will hereinafter be described indetail with reference to the drawings.

Referring now to the drawings, and in particular to FIG. 1, showntherein is a block diagram of an exemplary hardware configuration ofpart of an industrial machine, in the form of a forklift in accordancewith an embodiment of the present disclosure. In some embodiments, theindustrial machine is a conventional vehicle that is described and shownin block diagram form in U.S. Pat. No. 8,825,246. The followingdiscussion of FIG. 1 was modeled on the description of the forklifttruck in U.S. Pat. No. 8,825,246.

The following will describe a forklift truck as an industrial machineaccording to a first preferred embodiment of the present disclosure withreference to FIGS. 1 and 2. In the following description, the terms suchas “forward and backward”, “left and right” and “upper and lower”designate directions as viewed by an operator of the forklift truckseated in the operator's compartment and facing forward of the forklifttruck.

Referring to FIG. 1, reference numeral 10 designates a forklift truck asan industrial machine. The forklift truck 10 includes a truck body 11serving as a vehicle body of the present disclosure and a load handlingimplement 12 mounted to the front of the truck body 11. An operator'scompartment 13 is provided in the center of the truck body 11, and abattery 14 is accommodated in the truck body 11 under the operator'scompartment 13. The battery 14 may be provided by a lead-acid batteryhaving an electrolyte solution. Drive wheels 15 are arranged in front ofthe truck body 11 as front wheels, and steered wheels 16 are arranged inrear of the truck body 11 as rear wheels. A traction motor 17 is mountedin the truck body 11 for generating torque as an electric motor, as wellas generating power for charging the battery 14 (known as regenerativebraking) when the forklift truck 10 is slowing down. Power transmissionmechanism (not shown) is disposed between the traction motor 17 and thedrive wheels 15 for transmitting the torque to the drive wheels 15. Theforklift truck 10 of the first preferred embodiment is a battery-poweredforklift truck driven by electric power from the battery 14 mounted onthe truck body 11.

The load handling implement 12 has a mast assembly 18 including pairedouter masts 19 and inner masts (not shown). The pair of the left andright outer masts 19 has therebetween the paired inner masts that areslidable relative to the outer masts 19. Hydraulically-operated tiltcylinders 20 may be mounted to the outer masts 19, to permit the mastassembly 18 to be tiltable in the forward and backward directions of theforklift truck 10 by the operation of the tilt cylinders 20.Hydraulically-operated lift cylinders 21 may be mounted to the innermasts and the inner masts are slidably raised and lowered by theoperation of the lift cylinders 21. A pair of left and right forks 22are mounted to the mast assembly 18 through lift brackets 23 which arearranged so as to be raised and lowered relative to the inner masts. Thetruck body 11 is equipped with a loading pump (not shown) for supplyinghydraulic oil to the lift cylinders 21 and the tilt cylinders 20 and aload handling motor 24 as an electric motor for driving the loading pumpto lift the left and right forks 22, and as well as generating power forcharging the battery 14 (known as regenerative braking) when the leftand right forks 22 are being lowered.

An operator's seat 25 on which the operator of the forklift truck 10 canbe seated is mounted on a seat stand 26 in the operator's compartment 13of the truck body 11. A steering wheel 27 may be disposed in front ofthe operator's seat 25. A travel lever 28 is provided on the left sideof the steering wheel 27 and operated to select forward or backwardtravel of the forklift truck 10. A lift lever 29 is provided on theright side of the steering wheel 27 and used for operating the liftcylinders 21, and a tilt lever 30 is also provided on the same rightside of the steering wheel 27 for operating the tilt cylinders 20.

An accelerator pedal 31 may be provided on the floor of the operator'scompartment 13 for adjusting traveling speed of the forklift truck 10.Operation of the traction motor 17 may be controlled so that theforklift truck 10 travels at a speed corresponding to the degree towhich the accelerator pedal 31 is depressed by the operator. The truckbody 11 may be equipped with a controller 33 for performing variouscontrols of the forklift truck 10. A display unit 32 may be provided infront of the steering wheel 27 at such a position adjacent to the liftlever 29 and the tilt lever 30 that provides good visibility for theoperator.

The following will describe the electrical control of the forklift truck10 with reference to FIG. 2. The controller 33 is connected through aninterface 36 in a communicable manner to a drive circuit 34 thatcontrols the traction motor 17 and also to a drive circuit 35 thatcontrols the load handling motor 24. The traction motor 17 and the loadhandling motor 24 are connected through the respective drive circuits34, 35 to the battery 14 to receive power from the battery 14. Thetraction motor 17 is driven by the drive circuit 34 which is operable inresponse to commands from the controller 33, and the load handling motor24 is also driven by the drive circuit 35 which is operable in responseto commands from the controller 33. The drive circuits 34 and 35 alsopermit power generated by the traction motor 17 and the load handlingmotor 24 to be supplied to the battery 14 due to regenerative braking.The controller 33 serves as a motor controller of the present disclosureand has a central processing unit (CPU) (not shown) operable to performvarious control operations in predetermined procedures and a memory forstoring various data. A built-in memory (not shown) in the CPU of thecontroller 33 stores therein programs for a torque limiting conditionfor limiting the torque of the traction motor 17 gradually. The torquelimiting condition for the traction motor 17 serves as an electric motorlimiting condition of the present disclosure.

When equipped with the display unit 32, the controller 33 is connectedthrough an interface 37 in a communicable manner to the display unit 32provided in the operator's compartment 13. The display unit 32 has adisplay screen 40 displaying various information including time andserving as a display device of the present disclosure, a centralprocessing unit (CPU) 41, a real time clock IC 42, a memory 43 andcontrol switches 44. The CPU 41 is connected in a communicable manner tothe controller 33 through an interface 45, and various controls areperformed through the CPU 41 in predetermined procedures.

The display screen 40 displays battery information such as a capacity ofthe battery 14, warning messages such as a warning about parking brake,time-related information such as an accumulated time during which theforklift truck 10 is in key-on state, i.e. when a key is inserted in theforklift truck 10 and a selected traveling mode. The control switches 44include switches for displaying information, traveling mode selectionand setting of charging schedule. The traveling mode may be set instages in accordance with the load levels during traveling and loadhandling.

The real time clock IC 42 may be connected to the CPU 41 which providescurrent time and outputs the time data to the CPU 41. The real timeclock IC 42 may serve as a current time clock even when the forklifttruck 10 is in key-off state where the key is removed from the forklifttruck 10. Vehicle operating time according to one embodiment correspondsto the time elapsing while the forklift truck 10 is in key-on state andcalculated by the CPU 41 based on the time data of the real time clockIC 42. Thus, the CPU 41 serves as a vehicle operating time calculator ofthe present disclosure.

The memory 43 is connected to the CPU 41 and serves as a data-storingdevice of the present disclosure. The memory 43 stores data indicativeof the elapsed time and retains data even without being powered on. Forthe sake of convenience, the memory 43 is shown by a single memory inFIG. 2, but the memory 43 may be provided by plural memories. The memory43 may be provided by a rewritable non-volatile memory such asElectrically Erasable Programmable Read-Only Memory (EEPROM), but it isnot limited to the EEPROM. If the display unit 32 has a backup powersystem for constantly supplying power to the memory 43, the memory 43may be provided by a volatile memory, such as Random Access Memory (RAM)and a flash memory.

In accordance with the present disclosure, it is desirable to replacethe lead-acid battery 14 of the forklift truck 10 with a lithium-ionbattery pack 60. Some of the advantages of the lithium-ion battery pack60 over the lead-acid battery 14 is increased energy density resultingin longer operating life between charges, greater cycle life, constantpower and energy relative to various amounts of charge, enhanced depthof discharge, enhanced efficiency, and faster charging cycles. But,industrial machinery, such as the forklift truck 10, are used in awide-variety of temperatures, including temperatures below 15 degrees C.As discussed above, lithium-ion batteries can be destroyed by aphenomenon known as lithium plating when charged below 15 degrees C. Ifthe lead acid battery 14 were replaced with the lithium-ion battery pack60 and the forklift truck 10 was operated below 15 degrees C., theregenerative braking of the traction motor 17 and the load handlingmotor 24 would direct a charging current to the lithium-ion battery pack60 thereby destroying the lithium-ion battery pack 60.

As will be discussed below, the lithium-ion battery pack 60 is designedto be used as a replacement for the lead-acid battery 14 withoutrequiring significant changes to the remainder of the forklift truck 10,without disabling the regenerative braking functions of the tractionmotor 17 and the load handling motor 24, and without incurring theproblems associated with lithium plating.

As shown in FIG. 3, the battery pack 60 is provided with a lithiumbattery 62 having a plurality of battery units 70. By way of example,four battery units 70 are depicted in FIG. 4 and designated as 70-1,70-2, 70-3 and 70-n. It should be understood that the battery pack 60can have any number of battery units 70 and typically will have 28, 30,38, 40, 48, or 96 battery units 70. In the example discussed herein, thebattery pack 60 will have 96 battery units 70, connected in a 1P seriesconfiguration. The battery units 70 have a positive terminal 72 and anegative terminal 74. The battery units 70 can be combined in a seriesconfiguration in which the positive terminal 72 of one of the batteryunits 70 is connected to the negative terminal 74 of an adjacent batteryunit 70.

The battery pack 60 is also provided with an environmental managementcircuit 76 configured to regulate regenerative braking power to thebattery units 70 depending upon at least one environmental factor, suchas temperature. The environmental management circuit 76 will bedescribed hereinafter by way of example as monitoring temperature andregulating the regenerative braking power, but it should be understoodthat the environmental management circuit 76 can be configured tomonitor any other environmental factor that will affect charging of thebattery units 70.

In general, the environmental management circuit 76 is provided withsource terminals 80, battery terminals 82, a load 84, a semiconductordevice 86, a first environmental controlled switch 88, a secondenvironmental controlled switch 90, and a main switch 92. The sourceterminals 80 are provided with a positive terminal 80 a, and a negativeterminal 80 b. The battery terminals 82 include a first polarityterminal 82 a, and a second polarity terminal 82 b. The first polarityterminal 82 a is in series with the semiconductor device 86. Thesemiconductor device 86 includes a first terminal 96 and a secondterminal 98. Semiconductor device 86 is configured to only allow a flowof current in one direction, i.e. from the first terminal 96 to thesecond terminal 98. In one embodiment, the first terminal 96 is coupledto and in series with the first polarity terminal 82 a. In someembodiments, the semiconductor device 86 is a diode or a transistor.

In some embodiments, the load 84 is coupled in series with the sourceterminals 80, and also coupled in parallel with a combination of thelithium battery 62 and the semiconductor device 86. The load 84 isadapted to mimic resistance, amperage and voltage properties of thelithium battery 62, as well as receive and dissipate any power generateddue to regenerative braking. In one embodiment, the load 84 isimplemented as a series of diodes 100 a-n with each of the diodes 100a-n having a junction voltage, such as 0.7 V. The series of diodes 100a-n acts as a heat source when dissipating energy developed throughregenerative braking. Further, the plurality of diodes 100 a-n can bedistributed through the lithium battery 62 for uniformly heating thelithium battery 62. For example, the diodes 100 a-n can be mounted tobus bars within the lithium battery 62, so as to permit the transfer ofheat through the bus bars and into battery units 70 of the lithiumbattery 62. The number of diodes can be selected so as to receive anddissipate the power generated due to regenerative braking withoutinducing excessive current. Excessive current, as referred to herein,refers to an amount of current which can damage any component within thebattery pack 60, the drive circuits 34 and 35, the traction motor 17, orthe load handling motor 24. In one embodiment, the following formula isused to determine the number of diodes 100 a-n in the load 84.

No. of diodes=V_(b)/V_(j), where V_(b) is a voltage of the battery 62when charged, and V_(j) is a junction voltage of each of the junctionvoltages of the diodes 100 a-n.

In other words, when the sum of the junction voltages of the diodes 100a-n equal the voltage of the battery 62, then power from regenerativebraking can be directed to the diodes 100 a-n and dissipated withoutinducing excessive current.

The formula set forth above presumes that all of the junction voltagesare the same. This does not need to be the case, however, and diodes 100a-n having different, or a variety of junction voltages can be used. Theload 84 can also be implemented as a series of transistors, or a circuitdesigned to mimic the resistance, current and voltage properties of thelithium battery 62.

The first environmentally controlled switch 88 is coupled in parallelwith the semiconductor device 86. The second environmentally controlledswitch 90 is coupled in series with the load 84. The firstenvironmentally controlled switch 88 and the second environmentallycontrolled switch 90 are controllable, based upon an environmentalparameter between open and closed positions. When the environmentalparameter is in a first state, then the first environmentally controlledswitch 88 and the second environmentally controlled switch 90 are in afirst condition. In the first condition, the first environmentallycontrolled switch 88 is closed and the second environmentally controlledswitch 90 is open. When the environmental parameter is in a secondstate, then the first environmentally controlled switch 88 and thesecond environmentally controlled switch 90 are in a second condition.In the second condition, the first environmentally controlled switch 88is open and the second environmentally controlled switch 90 is closed.

For example, when the environmental parameter is temperature, apredetermined threshold can be used to delineate the first condition andthe second condition. The predetermined threshold can be between 5-20degrees Centigrade. For example, if the predetermined threshold is 15degrees centigrade, then temperatures 15 degrees centigrade or above maybe the first condition, and temperatures below 15 degrees centigrade maybe the second condition.

In the first condition, e.g., when the temperature of the battery 62 issufficient to avoid damage due to lithium plating, the firstenvironmentally controlled switch 88 is closed, and the secondenvironmentally controlled switch 90 is open. This causes current comingto and/or from the lithium battery 62 to pass the semiconductor device86 and to avoid the load 84. In the first condition, power can besupplied from the battery 62 to the traction motor 17 and the loadhandling motor 24, and power generated from regenerative braking issupplied to and recharges the lithium battery 62.

In the second condition, e.g., when the temperature of the lithiumbattery 62 is to low to permit recharging without damaging the lithiumbattery 62, the first environmentally controlled switch 88 is open, andthe second environmentally controlled switch 90 is closed. This causescurrent supplied by the battery 62 to pass through the semiconductordevice 86 and to avoid passing through the load 84 due to the sum of thejunction voltages being equal to the battery voltage V_(b). In thesecond condition, power can be supplied from the battery 62 to thetraction motor 17 and the load handling motor 24. Power generated fromregenerative braking that is directed to the battery 62, however, isblocked by the semiconductor device 86, and directed to the load 84 bythe closure of the second temperature controlled switch 90. The load 84dissipates the power generated from regenerative braking, by forexample, converting the power into heat. When the load 84 dissipates thepower generated from regenerative braking as heat, the load 84 can bethermally connected to the battery 62 so that the heat functions to warmthe lithium battery 62.

As the temperature of the lithium battery 62 increases beyond thepredetermined threshold, due at least in part to the heat supplied bythe load 84 into the lithium battery 62, the first environmentallycontrolled switch 88 and the second environmentally controlled switch 90are switched to the first condition to permit the regenerative power torecharge the battery 62 as discussed above.

The environmental management circuit 76 can also be provided with atleast one environmental sensor 110 and a controller 112. Theenvironmental sensor 110 is configured to sense an environmentalparameter, such as temperature, and to supply an electrical signal tothe controller 112 indicative of a level of the environmental parameter.For example, the environmental sensor 110 can be a thermocouple placedon or within the lithium battery 62 that generates an analog signaldependent upon the temperature of the lithium battery 62. The controller112 receives and interprets the signal, and then provides controlsignals, e.g., simultaneously, to the first environmentally controlledswitch 88 and the second environmentally controlled switch 90. In thisregard, the controller 112 includes logic to interpret the informationobtained from the environmental sensor 110 to determine whether thefirst environmentally controlled switch 88 and the secondenvironmentally controlled switch 90 should be placed into the firstcondition or the second condition. In some embodiments, the controller112 includes an analog to digital converter to convert analog signalsgenerated by the environmental sensor into a digital format. Thecontroller 112 can be implemented with circuitry. Circuitry, as usedherein, may be analog and/or digital components, or one or more suitablyprogrammed processors (e.g., microprocessors) and associated hardwareand software, or hardwired logic. Also, “components” may perform one ormore functions. The term “component,” may include hardware, such as aprocessor (e.g., microprocessor), and application specific integratedcircuit (ASIC), field programmable gate array (FPGA), a combination ofhardware and software, and/or the like. The term “processor” as usedherein means a single processor or multiple processors workingindependently or together to collectively perform a task.

Software may include one or more computer readable instructions thatwhen executed by one or more components cause the one or more componentto perform a specified function. It should be understood that algorithmsor process instructions described herein may be stored on one or morenon-transitory computer readable medium. Exemplary non-transitorycomputer readable medium may include random access memory, read onlymemory, flash memory, and/or the like. Such non-transitory computerreadable mediums may be electrically based, optically based, and/or thelike.

In one embodiment, the present disclosure describes a method ofupgrading a work machine, such as the forklift truck 10 having thelead-acid battery 14 coupled to a drive circuit 34 or 35 and at leastone motor 17 or 24. In this embodiment, the lead-acid battery 14 isremoved from the forklift truck 10, and the lithium-ion battery pack 60having the lithium battery 62 and the environmental management circuit76 is installed in the forklift truck 10 in circuit with the drivecircuit 34 or 35 and the at least one motor 17 or 24.

From the above description, it is clear that the inventive concept(s)disclosed herein are well adapted to carry out the objects and to attainthe advantages mentioned herein, as well as those inherent in theinventive concept(s) disclosed herein. While the embodiments of theinventive concept(s) disclosed herein have been described for purposesof this disclosure, it will be understood that numerous changes may bemade and readily suggested to those skilled in the art which areaccomplished within the scope and spirit of the inventive concept(s)disclosed herein.

What is claimed is:
 1. A method of upgrading a work machine having alead-acid battery coupled to a drive circuit and at least one motor,comprising the steps of: a. removing the lead-acid battery from the workmachine; and b. connecting a lithium-ion battery pack having a lithiumion battery and an environmental management circuit to the work machinein circuit with the drive circuit and the at least one motor.
 2. Themethod of claim 1, wherein the environmental management circuit includesa load having a plurality of diodes coupled in series.
 3. The method ofclaim 2, wherein the lithium ion battery has a battery voltage, and thediodes have junction voltages, and wherein a sum of the junction voltageof the diodes is at least equal to the battery voltage.
 4. The method ofclaim 1, wherein the environmental management circuit includes a firstenvironmentally controlled switch, and a second environmentallycontrolled switch, the first environmentally controlled switch coupledin parallel with a semiconductor device; and the second environmentallycontrolled switch coupled between a source terminal and a load, thefirst environmentally controlled switch and the second environmentallycontrolled switch being synchronized to switch between open and closedpositions subject to at least one environmental parameter being in afirst state or a second state, in the first state, the firstenvironmentally controlled switch is closed and the secondenvironmentally controlled switch is open.
 5. The method of claim 4,wherein in the second state, the first environmentally controlled switchis open and the second environmentally controlled switch is closed. 6.The method of claim 4, wherein the environmental parameter istemperature.
 7. The method of claim 6, further comprising: a temperaturesensor; and a controller coupled to the temperature sensor andconfigured to receive data from the temperature sensor indicative of atemperature, and synchronously control the first and secondenvironmentally controlled switches based upon the temperature sensed bythe temperature sensor.
 8. A method, comprising: monitoring temperatureof a lithium-ion battery pack; recharging the lithium-ion battery packwhen a temperature of the lithium-ion battery pack is above apredetermined temperature; and blocking energy directed to thelithium-ion battery pack when the temperature of the lithium-ion batterypack is below the predetermined threshold.
 9. The method of claim 8,wherein the predetermined threshold is in a range from 5-20 degreesCentigrade.
 10. The method of claim 8, wherein recharging thelithium-ion battery pack is defined further as directing energygenerated from regenerative braking generated by a work machine to thelithium-ion battery pack to recharge the lithium-ion battery pack. 11.The method of claim 8, wherein blocking energy directed to thelithium-ion battery pack is defined further as blocking energy directedto the lithium-ion battery pack by opening a first environmentallycontrolled switch, the first environmentally controlled switch inparallel with a semiconductor device configured to only allow a flow ofcurrent in one direction.
 12. The method of claim 11, wherein blockingenergy directed to the lithium-ion battery pack is defined further asdirecting the energy to a load coupled between source terminals.
 13. Themethod of claim 11, wherein blocking energy directed to the lithium-ionbattery pack is defined further as directing the energy to a pluralityof diodes coupled in series.
 14. The method of claim 11, whereinblocking energy directed to the lithium-ion battery pack is definedfurther as directing the energy to a load distributed through thelithium-ion battery pack to warm the lithium-ion battery pack.